一.環(huán)境配置
environment:
sdk: ">=2.12.0 <3.0.0"
dependencies:
flutter:
sdk: flutter
provider: 5.0.0
二.案例
1.create: (_): 后面要接一個(gè)新創(chuàng)建的暖混，而不能是已存在的變量
2.ProxyProvider被我用來(lái)把Counter的值轉(zhuǎn)換為另外一個(gè)值
3.${context.watch<Translations>().title} 是監(jiān)聽轉(zhuǎn)換后的代理值
4.() => context.read<Counter>().increment() 則是觸發(fā)數(shù)據(jù)源指向動(dòng)作
5.Provider狀態(tài)管理類似與React的Mobox，其實(shí)我理解都是交給Provider托管的
// ignore_for_file: public_member_api_docs, lines_longer_than_80_chars
import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
/// This is a reimplementation of the default Flutter application using provider + [ChangeNotifier].
void main() {
runApp(
/// Providers are above [MyApp] instead of inside it, so that tests
/// can use [MyApp] while mocking the providers
MultiProvider(
providers: [
ChangeNotifierProvider(create: (_) => Counter()),
ProxyProvider<Counter, Translations>(
update:(_,counter,__) => Translations(counter.count)
)
],
child: const MyApp(),
),
);
}
class Translations {
const Translations(this._value);
final int _value;
String get title => 'You clicked $_value times';
}
/// Mix-in [DiagnosticableTreeMixin] to have access to [debugFillProperties] for the devtool
// ignore: prefer_mixin
class Counter with ChangeNotifier, DiagnosticableTreeMixin {
int _count = 0;
int get count => _count;
void increment() {
_count++;
notifyListeners();
}
/// Makes `Counter` readable inside the devtools by listing all of its properties
@override
void debugFillProperties(DiagnosticPropertiesBuilder properties) {
super.debugFillProperties(properties);
properties.add(IntProperty('count', count));
}
}
class MyApp extends StatelessWidget {
const MyApp({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return const MaterialApp(
home: MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
const MyHomePage({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: const Text('Example'),
),
body: Center(
child: Column(
mainAxisSize: MainAxisSize.min,
mainAxisAlignment: MainAxisAlignment.center,
children: const <Widget>[
Text('You have pushed the button this many times:'),
/// Extracted as a separate widget for performance optimization.
/// As a separate widget, it will rebuild independently from [MyHomePage].
///
/// This is totally optional (and rarely needed).
/// Similarly, we could also use [Consumer] or [Selector].
Count(),
],
),
),
floatingActionButton: FloatingActionButton(
key: const Key('increment_floatingActionButton'),
/// Calls `context.read` instead of `context.watch` so that it does not rebuild
/// when [Counter] changes.
onPressed: () => context.read<Counter>().increment(),
tooltip: 'Increment',
child: const Icon(Icons.add),
),
);
}
}
class Count extends StatelessWidget {
const Count({Key? key}) : super(key: key);
@override
Widget build(BuildContext context) {
return Text(
/// Calls `context.watch` to make [Count] rebuild when [Counter] changes.
'${context.watch<Translations>().title}',
key: const Key('counterState'),
style: Theme.of(context).textTheme.headline4);
}
}
image.png
問題
1.空安全支持SDK 至少2.12.0（This requires the 'non-nullable' language feature to be enabled.）
2.Flutter 查看依賴包信息 flutter pub deps
image.png
參考:https://github.com/rrousselGit/provider/blob/master/resources/translations/zh-CN/README.md
